Add support for Op1 tablebase positions

[AttackingOrDefending]

Type of pull request:

• Bug fix
• Feature
• Other

Description:

Adds support for querying op1 tablebase positions. Details about op1 are here.

Related Issues:

None

Checklist:

• I have read and followed the contribution guidelines.
• I have added necessary documentation (if applicable).
• The changes pass all existing tests.

Screenshots/logs (if applicable):

[MarkZH]

Instead of this searching, you can directly query which squares the pawns are on. Something like

if white_pawns.popcount() != 1 or black_pawns.popcount() != 1:
    return False

wp = white_pawns.pop()
bp = black_pawns.pop()

return square_file(wp) == square_file(bp) and square_rank(wp) < square_rank(bp)

[MarkZH]

There are mistakes in my code. I thought op1 meant exactly one white pawn and one black pawn, not at least one of each. So, I'm probably wrong about searching not being necessary.

Also, white_pawns.popcount() should be len(white_pawns).

[MarkZH]

This actually works, I'll leave it to you to decide if it's easier to read.

    if not white_pawns or not black_pawns:
        return False

    for wp in white_pawns:
        for bp in black_pawns:
            if chess.square_file(wp) == chess.square_file(bp) and chess.square_rank(wp) < chess.square_rank(bp):
                return True

    return False

[AttackingOrDefending]

Switched as it seems cleaner.